The present application claims priority to Japanese Application(s) No(s). P2000-368634 filed Dec. 4, 2000, which application(s) is/are incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a liquid crystal display device having a field light emission layer driven by electrodes on a pair of opposing substrates.
2. Description of the Related Art
The liquid crystal display device along with having a lighter and thinner shape than display devices such as utilizing cathode ray tubes, further has low power consumption and so is used in display devices on portable information terminals, etc.
Display devices for portable information terminals must be lightweight, thin, and along with low power consumption must also have a display easily visible in all kinds of environments. However among the various liquid crystal display devices of the related art, transmittance type liquid crystal displays have backlighting (backlit display) that makes them easily visible in dark surroundings yet makes the transmittance type liquid crystal display nearly impossible to see when under an extremely bright external light such as sunlight.
Reflective liquid crystal display devices on the other hand, though easy to see in brightly lit surroundings have the disadvantage of being hard to view in dark surroundings. Front lighting with light guide plates above the liquid crystal panel therefore had to be installed in these reflective liquid crystal display devices. However, using this front lighting brings the problems of lower reflectance, lower contrast and projection of external light, etc.
To resolve the problems with the transmittance type liquid crystal display devices and reflective type liquid crystal display devices, a semipermeable reflective liquid crystal display device incorporating a transmittance display and a reflective display into one liquid crystal display device was developed that allowed a portion of the backlight to transmit through, and reflected a portion of the surrounding (ambient) light. However the display characteristics of this liquid crystal display device were inadequate because light transmittance was worse than in transmittance liquid crystal display devices of the related art, while the reflectivity of the display was worse than reflective liquid crystal display devices of the related art. The light transmittance ratio was particularly low so that the brightness dropped drastically when transmitting an image through the screen during transmittance mode display. Compensating for the drop in brightness required increasing the backlight brightness causing the problem of higher power consumption.
Further, installing backlighting or a frontlight in the liquid crystal display device increased the module thickness and weight making it unsuitable for use in portable information terminals.
Self-luminescent elements such as used in electroluminescent display devices on the other hand, had features such as thinness, lightweight and high contrast as well as high brightness allowing use even in environments that were somewhat bright. These device characteristics led to expectations that self-luminescent elements would be ideal for use in portable information terminals.
However electroluminescent display devices using electroluminescent elements were also subject to drastic drops in recognizability under extremely strong external light such as sunlight. These devices also had the drawback of power consumption much larger than semireflective display devices. Electroluminescent elements had the further disadvantages of a short operational life and were unable to with stand long-term use.
To resolve the above-mentioned problems in the liquid crystal display devices and electroluminescence display devices, a display device having an organic electroluminescent element in the rear of the display device was disclosed in Japanese Patent Laid-Open No. Hei 9-50031 and Japanese Patent Laid-Open No. Hei 10-125461. These display devices utilize a reflective liquid crystal display device in bright surroundings, and transmittance type liquid crystal display device backlit with organic electroluminescent elements in dark surroundings. All of the pixels are used during a reflective display and all of the pixels are used for transmittance display so a high quality display could be obtained in different surroundings.
However, the light source comprised of organic electroluminescent elements was separate from the liquid crystal display device creating the problem of a module that was too thick and heavy. Also, the light source of organic electroluminescent elements was always lit up in dark surroundings, causing the problem that operational life was short.
In Japanese Patent Laid-Open No. Hei 11-249133 and Japanese Patent Laid-Open No. Hei 11-305224 on the other hand, technology was disclosed for mounting organic electroluminescent elements on the upper surface of a reflective type liquid crystal display device. These display devices attempted to resolve the problem of the front light in the related art. The structure described in Japanese Patent Laid-Open No. Hei 11-249133 required a deflection plate between the organic electroluminescence layer and the liquid crystal display device. However, forming an organic electroluminescent layer on the deflection plate was difficult. Making a deflection plate on the inner side of the transparent substrate of the liquid crystal display device was also possible however this method was not practical since the device characteristics were worse than the film type deflection plate of the related art.
The structure described in Japanese Patent Laid-Open No. Hei 11-305224 required high-precision alignment so that the metallic electrode of the organic electroluminescence element would not overlap the aperture of the liquid crystal display device. Further, an organic electroluminescence element was formed across the entire upper surface of the liquid crystal panel so that the problems of low reflectivity, low contrast and external light projection occurred, the same as in the liquid crystal display device of the related art formed with a front light.
The present invention has the object of resolving the problems in liquid crystal display devices of the related art having a backlight or front light or liquid crystal display devices of the related art utilizing an organic electroluminescence element as a light source; and providing a liquid crystal display device capable of a high quality display in either bright or dark surroundings, having a thin, lightweight shape and low power consumption, and ideal as a display device for portable information terminals.
In the present invention, a field light emission layer separate from the liquid crystal layer is formed between a pair of substrates comprising the liquid crystal panel or the field light emission layer is formed jointly with the liquid crystal layer, and turning this field light emission layer on and off by driving the electrodes of the liquid crystal layer eliminates the need for a front light or back light and a thin, lightweight structure can be obtained in an extremely simple structure. Further, in bright surroundings, a reflective display is shown utilizing external light, and in dark surroundings a display is shown by emitting light from the field light emission layer. The field light emission layer does not continually emit light during the display in dark surroundings so power consumption is also reduced.
The present invention in other words, provides a liquid crystal display device comprised of a pair of substrates having electrodes on mutually opposing facing sides, and a liquid crystal layer enclosed by the pair of substrates, and displaying a dark screen when no electrical field is applied to the liquid crystal layer, wherein a field light emission layer driven by the electrodes is formed between the pair of substrates.
Particularly a first embodiment of the liquid crystal device, is provided wherein a field light emission liquid crystal material layer is formed as a combined liquid crystal layer and field light emission layer, and in a second embodiment, a liquid crystal layer is formed separately from the field light emission layer.
A manufacturing method for a liquid crystal device of the first embodiment of the present invention is provided for attaching together a pair of substrates having electrodes on one side, with the electrodes facing each other, injecting liquid crystal material between both substrates, in a liquid crystal device displaying a dark screen when no electrical field is applied to the liquid crystal layer, wherein a field light emission liquid crystal material is injected as the liquid crystal material.
A manufacturing method for a liquid crystal device of the second embodiment of the present invention is provided for attaching together a pair of substrates having electrodes on one side, with the electrodes facing each other, injecting liquid crystal material between both substrates, in a liquid crystal device displaying a dark screen when no electrical field is applied to the liquid crystal layer, wherein before attaching the substrates together, a field light emission layer is formed on the electrode of one substrate.
The present invention further provides a liquid crystal display terminal as a portable information terminal having a liquid crystal display device, wherein the liquid crystal display device is composed of a pair of substrates having electrodes on mutually opposing facing sides, and a liquid crystal layer held by the pair of substrates, and the liquid crystal device displays a dark screen when no electrical field is applied to the liquid crystal layer, wherein a field light emission layer driven by the electrodes is formed between the pair of substrates.
The liquid crystal display device of the present invention has the same reflective display in bright surroundings as the reflective type liquid crystal display device of the related art, and in a display in dark surroundings the field light emission layer emits light so that back lights and front lights are unnecessary and an extremely simple thin and lightweight structure can be achieved. Also, the entire pixel range is effectively utilized during both a reflective display and a light emission display. The liquid crystal display device of the present invention is therefore lighter in weight and thinner than liquid crystal display devices of the related art having front lighting or back lighting, and also provides a fine quality display.
Also in the liquid crystal display device of the present invention, the field light emission layer does not continually emit light during light emission display in dark surroundings, light is emitted from the required pixels according to the switching of the liquid crystal layer. The power consumption of the liquid crystal display device of the present invention is therefore low compared to electroluminescence display devices of the related art, and the operational service life is longer.